chapter 10: reaction rates and equilibrium

Question 1

what is the definition of rate of reaction?

Answer 1

the change in concentration of a reactant or product in a given time.

Question 2

what is the equation for rate of reaction?

Answer 2

rate = change in concentration/time

Question 3

what are the units for rate of reaction?

Answer 3

mol dm-3 s-1

Question 4

what is collision theory?

Answer 4

for a reaction to occur, particles need to collide with sufficient energy and the correct orientation.

Question 5

what are the factors that affect rate of reaction?

Answer 5

concentration (if liquid)
pressure (if gas)
temperature
surface area
presence of a catalyst

Question 6

how does rate of reaction change as the reaction progresses?

Answer 6

1. rate of reaction is fastest at the start, each reactant is at its highest concentration.
2. rate slows down as the reaction proceeds, reactants are being used up and their concentrations decrease.
3. when one of the reactants is used up, concentrations stop changing and rate of reaction is zero.

Question 7

how does increasing concentration affect the rate of reaction?

Answer 7

rate of reaction increases.
there are more particles in the same volume, so they are closer together and collide more frequently.
there are more efficient collisions so a faster rate of reaction.

Question 8

how does increasing pressure affect rate of reaction?

Answer 8

rate of reaction increases.
same number of gas molecules occupy a smaller volume, so they collide more frequently.
more effective collisions in the same time.

Question 9

how does increasing temperature affect rate of reaction?

Answer 9

particles have more energy so there are more frequent collisions.
more of these collisions are over the activation energy.
rate of reaction increases.

Question 10

how does increasing surface area affect rate of reaction?

Answer 10

increases rate of reaction.
more area for collisions to take place so more frequent and effective collisions.

Question 11

how does a catalyst affect rate of reaction?

Answer 11

increases rate of reaction.
provides an alternative pathway with a lower activation energy.

Question 12

what methods can be used to monitor the progress of a reaction?

Answer 12

monitoring the removal of a reactant.
following the formation of a product.

Question 13

what methods can be used to determine the rate of a reaction that produces a gas?

Answer 13

monitoring the volume of gas produced at regular time intervals using gas collection.
monitoring loss of mass of reactants using a balance.

Question 14

what is activation energy?

Answer 14

the minimum energy required to start a reaction by breaking the bonds

Question 15

what is a catalyst?

Answer 15

a substance that changes the rate of a chemical reaction without undergoing a permanent change. It lowers the activation energy of the reaction by providing an alternative reaction pathway.

Question 16

what is a homogeneous catalyst?

Answer 16

a catalyst that has the same physical state as the reactants.
The catalyst reacts with the reactants to form an intermediate
The intermediate then breaks down to give the product and regenerates the catalyst

Question 17

what are 2 examples of homogeneous catalysts?

Answer 17

1. making esters with sulfuric acid as a catalyst.
   the reactants and catalyst are all liquid.
2. ozone depletion with Cl radicals as the catalyst.
   reactant and catalyst are gases.

Question 18

what is a heterogeneous catalyst?

Answer 18

a catalyst that has a different physical state from the reactants.
Usually solids in contacts with gaseous reactants or reactants in solution.
Reactants molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction then takes place.
After reaction, the product molecules leave the surface of the catalyst by desorption.

Question 19

what are some examples of heterogeneous catalysts?

Answer 19

Haber process
reforming
hydrogenation of alkenes

Question 20

what is the process of a heterogeneous catalyst?

Answer 20

absorb
react
desorb

Question 21

what are the benefits of using catalysts in industrial processes?

Answer 21

1. they reduce activation energy which reduces temperature needed and energy needed.
2. less energy needed, so less fossil fuels and electricity used, this is cheaper.
3. using less fossil fuels helps with the issue of global warming.

Question 22

what are some drawbacks of catalysts?

Answer 22

expense
unsafe disposal

Question 23

what is the Boltzmann distribution?

Answer 23

spread of molecular energies.
In a gas, a liquid, or a solution, some molecules move slowly with low energy and some molecules move fast with high energy.
Most molecules move close to the average speed and have close to the average energy.